Internal combustion engines have been used for many years for providing motive power for driving a vehicle. Most vehicles on the road today are provided with either a four, six, or eight cylinder engine which is selected based upon the typical torque demand requirements for the individual type vehicle being designed. For example, four cylinder engines are typically used for commuter vehicles which are compact and typically have low load requirements and limited performance expectations. Six cylinder and eight cylinder engines are typically employed in larger vehicles wherein larger load carrying capacity and higher performance are expected. Some of the existing vehicle designs have suffered from low fuel efficiency due to the fact that the internal combustion engine for the vehicle has to be designed with a sufficient capacity to meet the high torque demands that are only occasionally required.
The dual crankshaft engine of the present invention overcomes these deficiencies by providing a powertrain system that includes a dual crankshaft engine with one of the engine portions being independently operable for providing driving torque to a transmission while the second engine portion can be utilized to supplement the driving torque of the first engine portion to meet higher torque demand requirements. Operation of the dual crankshaft engine is provided such that during normal driving at constant speeds and typical driving loads, the first engine portion is utilized for providing driving torque to the wheels of the vehicle. During periods of operation where increased levels of torque are required, such as during acceleration, pulling a heavy load, or climbing a hill, the second engine portion is operated in conjunction with the first engine portion for meeting the higher torque demand requirements. A coupling arrangement is provided for connecting the first and second crankshafts for starting the second engine portion and also for engaging the first and second crankshafts together in phase with one another. In order to effectively control this dual crankshaft engine, a control strategy is provided that efficiently and effectively determines when and how to couple the second engine to the first engine.